A cooler of the aforementioned kind is known from EP 1 774 236 where compressed air from a separate system can be intermittently injected into the material on the grate with a view to removing any agglomerates and so-called snowmen formations which have been formed by clogging of clinker material, and causing decreased efficiency of the cooler and where the duct for cooling gases through the use of an appropriate valve arrangement in the form of for example a tilting damper is blanked off when compressed air is injected. The disadvantage of this known cooler is that the valve arrangement is a mechanically movable component which may wear out relatively quickly when exposed to compressed air in expansion, consequently giving rise to operational problems.